It affects the layers of the earth the ozone layer which protects us from the sun can't protect very good. Which increases the tempature here on earth.
Explanation:
In the majority of cases, the extra copy of chromosome 21 comes from the mother in the egg.
In a small percentage (less than 5%) of cases, the extra copy of chromosome 21 comes from the father through the sperm.
In the remaining cases, the error occurs after fertilization, as the embryo grows.
Subtract the atomic number from the atomic mass to get the neutrons
